Interlocking circuits



March 28; 1939.

o..-H. SCHADE INTERLOCKING CIRCUITS Original Fi led Bed. 15, 1935 llllll IVIY" INVENTOR 0770 hi. SCl-IAOE ATTORNEY Patented Mar. 28, 1939 UNITED STATES INTERLOCKING CIRCUITS Otto H. Schade, West Orange, N. J assignor to Radio Corporation of America, a corporation of Delaware Original application December 15, 1933, Serial No. 7 02,451. Divided and this application February 15, 1936, Serial No. 64,050

6 Claims. (01. 179-111) The present invention relates broadly to energizing circuits for amplifiers utilizing electronic tubes and more particularly to novel interlocking .circuit arrangements for bias rectifiers. This application is a division of my co-pendihg application #702,451 filed December 15, 1933 now U. S. Patent No. 2,037,659.

Vacuum tube amplifiers require supply voltage sources for input (C-bias voltage) and output (B-voltage) circuits that are substantially independent of one another, at least within the amplified frequency range. Filter networksare commonly used to prevent A. C. reactions between B and C voltages if both are taken from a single supply source. In the case of very low frequency amplification these filter networks assume large proportions and finally cease to operate at zero frequency. Class B operation of amplifier tubesat varying signal intensities, such as in broadcasting, causes considerable variation of the B supply current which in turn causes fluctuations of the B supply voltage. The magnitude of these fiuctuations depends on the internal resistance of the B supply source. It is well known that variations of the C bias voltage has a considerable greater efiect 0n the performance of the amplifier than variations of the B voltage. Obviously then, when the same source is utilized for the C and B voltage supply slight variations in the C bias voltage caused by variations of the B supply current produce undesirable effects. Superior results are, therefore, obtained with biased low frequency amplifiers, especially, those of the overbiased type (Class A-B or Class B) if a separate voltage supply system for bias voltages is provided. In accordance with the present invention the bias voltage is conveniently supplied from a separate rectifier circuit. The power required is usually small so that a vacuum tube rectifier of relatively low saturation current may be used successfully for this purpose.

In a particular practical embodiment of the invention it was found that utilizing one diode contained in a type 55 amplifier tube gave commendable results. If a separate rectifier tube or diode is used to furnish bias voltage to other amplifier tubes it is necessary to provide means 50 for interlocking the bias rectifier and the other amplifier tubes in such a way that removal of the'rectifier tube and thus taking off the bias voltages, does not cause destructions in the tubes normally receiving bias voltage from this rectifier. 55 Objects of the invention are to provide simple but efiectiveinterlocks between the biased tubes and the bias rectification circuits so that the power tubes may be protected. Still other ob:-

jects of the invention are to improve generally the simplicity and efliciency of energizing cir- 5, cuits for vacuum tubes and particularly to provide an economical and compact form of bias rectifiers and interlocking arrangements for amplifier circuits and the like .which is not only reliable in operation but may be economically 10 manufactured and assembled. The novel features which are believed to be characteristic of the invention are set forth in particularity in the appended claims.

The invention itself, however, both as to its 15 organization and method of operation will best be understood by reference to the'following description taken in connection with the drawing in which there is indicated diagrammatically several circuit arrangements whereby theinventio-n 20 may be carried into efiect.

The single figure in the drawing illustrates a form of the invention wherein a separate bias rectifier of the full wave type is used and wherein the tubes to be biased become self-biased'if 25 the separate bias rectifier is removed at which time the filament circuit of the power tubes is opened.

Broadly construed the inventionv described in said copending application #702,451 provides three methods of protective interlocks. The first of these methods which is illustrated generally by'Figure 1 of said copending application provides a bias rectifier and plate voltage rectifier enclosed within a single envelope. The cathodes of both of these rectifiers are heated by the same current. In other words, the heating circuits are in series. The interlock is'provided by reason of the. fact that one of the rectifiers cannot be 40 removed without the other since they are both within a single enclosure; also a burn-out of the heater will affect both rectifiers simultaneously, since, as previously stated, the heating circuits are in series and the same current traverses both thereof. r

The second method utilizes a bias rectifier (diode) which is contained in the envelope of the tube receiving the bias voltage. Both Figures 2 and 3 of the copending application illustrate this method. It is'quite obvious from a consideration of the drawing that the bias rectifier can'- not be removed without removing the tube and further that a heater burn-out afiects both the bias rectifier and the tube receiving the bias voltage since they both have the same cathode.

The third method incorporates a separate bias rectifier tube and is illustrated generally by Figure 4 of the copending application. The interlock in this case is provided by means of a socket contact, openingthe filament circuit of the biased tubes and removing a short-circuit across a selfbias resistor. one of the heater pins of the bias rectifier in connection with two auxiliary pins thereof. On removal of the bias rectifier tube a self-bias resistor is, so to speak, thrown in and provides a bias voltage for the tubes. At the same time the filament circuit of these tubes is opened so that the cathodes thereof become cold orat least have a lower temperature when the bias rectifier is re-installed in the socket. In this arrangement as the bias rectifier does not provide a bias voltage until its cathode starts to emit, the amplifier tubes may draw relatively heavy plate currents if the biased rectifier is quickly replaced by a cold tube (the self-bias resistor is shorted when the bias rectifieris inserted), hence, the bias rectifier tube should have a short heating time so as to shorten the time of overload current on the amplifier tubes to a minimum.

. However, it has been found in practice that an exchange of the bias rectifier tube requires sufiicient time to lower the emission of the amplifier tubes sufiiciently to prevent severe overload currents.

It should be understood that while the energy for the bias voltage rectifier has been shown as derived from the commercial power supply mains or power transformer it should be understood that any suitable source may be utilized for this energy, as for instance, the local oscillator in superheterodyne receivers.

The interlock in the case of Figure 1 of the parent application is provided by reason of the fact that the bias rectifier which is shown as the half wave rectifier cannot be removed without removing the B supply rectifier or the full wave rectifier. Also, in view of the fact that the heater circuits are connected in; series a burn-out in onewill necessarily disable the other as previously disclosed.

In the drawing of the present application a biasing rectifier tube T7 is provided having four pins 62, 63, 64 and 65. The pins 62 and 63 are utilized to feed energy to the heating element 6|. Cooperating with the heatingelement 6| are two cylindrical cathodes '51 and 58, thesebeing connected to points 56 and 54 respectively of the secondary 26. The midpoint 55 of the secondary 26 is grounded as at G. Tube T7 is also provided with a pair of anodes 59 and B0. Anode 59 cooperates with the cathode 58, whereas, anode 66 cooperates with the cathode 51. The two anodes are connected together. A common conductor 13 connects the two anodes to the midpoint of the secondary of input transformer 36. The bias for the tubes T5 and To is provided by reason of the fact that the drop across the bias resistor 12 fed by rectifier T7 is impressed upon the-grid circuits of the tubes T5 andTe. The rectifier tube T7 may be considered as affull wave rectifier in inverse relation to the rectifier T2 so that the potentials developed by the rectifier T7 are negative and may be utilized for biasing purposes. Condenser H is provided to by-pass the applied A. C. voltage so that it does not develop a large ripple voltage across resistor 72. The portion be tween terminals 56 and 54 of secondary 26 is uti- The socket contacts are made by lized for feeding the A. C. to the cathodes 5 1 and 58 of rectifier T7. The secondary 53 is utilized to furnish current to the heaters of tubes T5 and Ta as well as to the heater element 6| of tube T1 and is additionally provided with terminals 66 and 61 for feeding energizing currents to any other heaters of the system. A self-bias resistor 15 is connected across the conductors 69 and 10 from pin terminals 64 and 65 respectively so that upon removal of the tube T: from its socket the resistor 15 comes into play as a self-bias for the tubes T5 and T6 and thus prevents damage to the tubes while the cathodes thereof remain hot. It should be noted that removal of the tube T: from its socket not only breaks the circuit at points 62 and 63 but also breaks the circuit at points 64 and 65 so that the short-circuit across resistor 15 is removed. When the tube T'zis again replaced in its socket a short-circuit is provided across the resistor 15, thus preventing its afiect ing tubes T5 and T6.

The interlock in the circuit arrangement described is provided by reason of the fact that the removal of tube T7 breaks the filament circuit of the amplifier tubes T5 and T6 and further conditions resistor 15 so as to act as a self-bias to protect the tubes T5 and Te while the cathodes thereof remain hot.

As shown in the drawing, the tube T2 is a full wave rectifier which is adapted to be connected to a suitable source of electrifying current through the transformer PT and terminals I and 2. To the output of the full wave rectifier T2 is connected a filter circuit comprising a choke coil 76 and a filter condenser 11. The cathode of the tube T2 is connected to the anodes of the tubes T5 and T6 in customary fashion, while the center point of the secondary 26, the ends of which are connected respectively to the two anodes of tube T2, is connected to the cathodes of tubes T5 and T6 through the ground connection. In this way it will be seen that the output of the rectifier tube T2 furnishes the tubes T5 and Te through the ground connection. In this way it will be seen that the output of the rectifier tube T2 furnishes the tubes T5 and T6 with anode current.

While there has been indicated and described certain specific arrangements for carrying the invention into effect it will be apparent to anyone skilled in the art that the invention is by no means limited to the particular organizations shown and described but that many modifications may be made without departing from the scope of the invention as set forth in the appended claims.

I claim:

1. In an amplifier circuit, an electronic tube provided with anode, cathode and grid electrodes, a source of alternating current energy, a rectifier and filter circuit arrangement for supplying space current to said tube, a bias resistor associated with both the anode to cathode circuit and signal grid to cathode circuit of the amplifier tube to provide an automatic bias for said tube, a second rectifier coupled to said source, a receptacle for said second rectifier, connections between the second rectifier output and said grid electrode of said tube for biasing said grid. with respect to the cathode of the tube, a heater circuit for the cathode of said tube said heater circuit being coupled to said source, means associated with the second rectifier receptacle for breaking the heater circuit upon removal of the second rectifier from its receptacle, and means for short-circuiting the bias resistor when the second rectifier is inserted in the receptacle and for breaking the short-circuit upon removal of the second rectifier from the receptacle.

2. In a relay circuit having at least one electronic tube provided with an anode, an indirectly heated cathode and a grid electrode, a power conditioning circuit including a pair of input terminals for connecting the conditioning circuit to a commercial power outlet, said power conditioning circuit including a first rectifier unit and a filter circuit for supplying the electronic tube with anode current, a second rectifier unit for supplying the grid electrode with bias potential, said second rectifier unit including a tube having an indirectly heated cathode and an anode, a socket for said last named tube, heater means for said indirectly heated cathodes, an energizing circuit for the heater means, means associated with said last named tube and said socket for breaking the energizing circuit for the heater means of the first named cathode when the second rectifier tube is removed from its socket to thereby disable said electronic tube.

3. In a relay circuit having at least one electronic tube providedwith an anode, a cathode and a grid electrode, a power conditioning circuit including a pair of terminals for connecting the conditioning circuit to an alternating current power outlet, said power conditioning circuit including a first rectifier unit and a filter circuit associated therewith for supplying the electronic tube with anode current, a second rectifier unit and filter means associated therewith for supplying the grid electrode of said tube with bias potential, said electronic tube being provided with an input circuit and an output circuit, an automatic bias resistor connected in both the input and output circuits of said electronic tube, a resistance element connected between the control electrode and the cathode of said tube, said second rectifier unit including a rectifier tube socket adapted to receive a rectifier tube, a switching means operably associated with the socket and the rectifier tube, an energizing circuit for the cathode of the electronic tube including said switching means, said switching means being operable to short circuit the automatic bias resistor and to connect the output of the second rectifier unit across said resistance element when the rectifier tube is in its socket, and to remove the short circuit across the automatic bias resistor and break the cathode energizing circuit when the rectifier tube is removed from its socket.

4. In combination, a thermionic tube, means whereby space current in said tube furnishes a grid-biasing potential thereto, additional means for furnishing grid biasing potential to the tube, and means providing connections. between said first mentioned and additional means whereby, when the additional means is active, the first mentioned means is automatically rendered inactive.

5. In combination, a thermionic tube, means whereby space current in said tube furnishes a grid biasing potential thereto, additional means including a rectifier circuit for furnishing grid biasing potential to the tube, and means providing connections between said first mentioned and additional means. whereby when the rectifier tube is active the first mentioned means is automatically rendered inactive.

6. In combination, a thermionic tube having an input circuit and an output circuit, means, including a bias resistor in both said circuits, whereby space current in said tube furnishes a grid biasing potential thereto, an additional means including a circuit provided with a removable rectifier tube for furnishing grid biasing potential to the first mentioned tube and means providing connections between said first mentioned and additional means whereby when the additional means is active the first mentioned means is automatically rendered inactive and when the rectifier tube is removed from the circuit the first mentioned means is automatically rendered active and the thermionic tube is rendered inactive.

OTTO H. SCHADE. 

